Apparatus for detecting the entry of formation gas into a well bore

ABSTRACT

In the representative embodiments of the apparatus of the present invention disclosed herein, one or more unique sampling devices are arranged between the upper and lower telescoping members of a typical slip joint which is tandemly connected in the drill string preferably a short distance above the drill bit. Each of these fluid samplers includes telescoping piston and chamber members defining an enclosed sample chamber which is expanded in response to extension of the slip joint members. Valve means are cooperatively arranged with each of the sampling devices for admitting a predetermined volume of drilling mud into the sample chamber each time the slip joint is extended. By moving the drill string so as to expand the sampling chamber, the pressure of the entrapped sample is reduced to at least the saturation pressure of a gas-containing drilling mud at the borehole ambient temperature. By measuring the force required to expand the sampling chamber, the presence or absence of formation gas in the drilling fluid can be determined; and, if desired, these force measurements may be used to derive quantitative measurements which are representative of the percentage of gas entrained in the discrete sample.

United States Patent [191 Tanguy et al. 1 1 Apr. 9, 1974 1 APPARATUS FORDETECTING THE ENTRY [57] ABSTRACT OF FORMATION GAS INTO A WELL BORE [75]Inventors: Denis R. Tanguy; Joseph F. Kishel, In the representativeembodiments of the apparatus of 7 both of Clarks Summitt, Pa. thepresent invention disclosed herein, one or more unique sampling devicesare arranged between the [73] Asslgnee' 33 Instruments Newark upper andlower telescoping members of a typical slip joint which istandemlyconnected in the drill string [22] Filed; May 17, 1973 preferably ashort distance above the drill bit. Each of these fluid samplersincludes telescoping piston and [211 App! 36lll1 chamber membersdefining an enclosed sample cham- Related US. Application Data her whichis expanded in response to extension of the [60] Division of 242,320April 0, 1972 which slip joint members. Valve means are cooperativelyaris a continuation-in-part of Ser. No. 105,885, Jan. 12, ranged witheach of the Sampling devices for admitting 1971, abandoned. apredetermined volume of drilling mud into the sample chamber each timethe slip joint is extended. By [52] US. Cl 166/107, 166/162, 166/264,moving the drill string so as to expand the sampling 175/233 chamber,the pressure of the entrapped sample is re- [51] Int. Cl E2lb 27/00,E2lb 47/00 ced to at least the saturation pressure of a gas- [58] Fieldof Search 166/264, 162, 107; Containing drilling mud at the boreholeambient tem- 175/232, 233, 317, 318, 321 perature. By measuring theforce required to expand the sampling chamber, the presence or absenceof for- [56] References Cited mation gas in the drilling fluid can bedetermined; UNITED STATES PATENTS and, if desired, these forcemeasurements may be used 2 418 500 4/1947 Chambers 175 233 to derivequantitative measurements which f 2:785:756 3/1957 Reynolds I I I i166/107 sentatwe of the percentage of gas entramed 1n the dis- 3,621,92511/1971 Reynolds 175/232 Crete sample- 8 Claims, 17 Drawing FiguresPAIENTEUAPR- slam 3.802.502

' sumuors FIG. 6A

/ //W\\\\WL 2 m PAIENTEDAPR 91914 FIG. 8

SHEU 6 OF 6 APPARATUS FOR DETECTING THE ENTRY OF FORMATION GAS INTO AWELL BORE This application is a division of US. Pat. application Ser.No. 242,320, filed Apr. 10, 1972, which was itself acontinuation-in-part of US. Pat. application Ser. No.

1 105,855, filed .Ian. I2, 1971, and now abandoned.

Those skilled in the art will, of course, appreciate that while drillingan oil.or gas well, a drilling fluid or so-called .mud is customarilycirculated through the drill string and drill bit and then returned tothe surface by way of the annulus defined between the walls of theborehole and the exterior of the drill'string. In addition to coolingthe drill bit and transporting the formation cuttings removed thereby,the mud also functions to maintain pressure control of the various earthformations as they are penetrated by the drill bit. Thus, it iscustomary to selectively condition the drilling mud for maintaining itsspecific gravityor density at a'sufficiently high level where thehydrostatic pressure of the column of mud in the borehole annulus willbe sufficient to prevent or regulate the flow of high-pressure connatefluids which may be contained in the formations being penetrated by thedrill bit.

It is, however, not at all uncommon for the drill bit to unexpectedlypenetrate earth formations containing gases at pressures greatlyexceeding the hydrostatic head of the column of drilling mud at thatdepth which will often result in a so-called blowout. It will beappreciated that unless a blowout is checked, it may well destroy thewell and endanger lives and property at the surface. Thus, to beabundantly safe, it might be considered prudent to always maintain thedensity of the drilling mud at excessively high levels just to preventsuch blowouts from occurring. Those skilled in the art will appreciate,however, that excessive mud densities or so-called mud weightssignificantly impair drilling rates as well as quite often unnecessarilyor irreparably damage potentially producible earth formations which areuncased. As a matter of expediency, therefore, it is preferred that thedrilling mud be conditioned so as to maintain its density at a levelwhich is just sufficient to at least regulate, if not prevent, theunexpected entry of high-pressure formation fluids into the borehole andinstead rely upon one or moreof several typical operating techniques forhopefully detecting the presence of such formation fluids in theborehole.

Many techniques have, or course, been proposed for detectingthe-presence of such high-pressure fluids in the borehole with varyingdegrees of accuracy. For example, detection techniques which may be usedinclude observing changes in the rotative torque as well as thelongitudinal drag on the drill string, monitoring differences betweenthe flow rates of the inflowing and outflowing streams of the drillingmud as well as'measuring various properties of the returning mud streamand the cuttings being transported to the surface thereby. Those skilledin the art will appreciate, however, that none of the several techniqueswhich are presently employed will reliably and immediately detect theentry of high-pressure gases into the borehole. For example, variationsof torque or drag on the drill string are not always reliableindications since borehole conditions entirely unrelated to the presenceof highpressure gases in the borehole mud can be wholly responsible forcausing significant variations in these parameters. On the other hand,although such techniques as monitoring of the mud flow rates ormeasuring the physical characteristics of the returning mud stream maywell reliably indicate the entrance of high-pressure formation gasesinto the borehole, the interval of time required for a discrete volumeof mud containing such gases to reach the surface may well be in theorder of several hours. This, of course, will usually be too late topermit preventative measures to be taken to avoid a disastrous blowout.

Accordingly, it is an object of the present invention to provide new andimproved apparatus for reliably detecting the entrance of even minoramounts of formation gas into a borehole being drilled and thenimmediately providing a positive indication at the surface that suchgases are present.

This and other objects of the present invention are attained byarranging the new and improved apparatus described and claimed herein toeach include a pair of telescoped members which are adapted to betandemly coupled in a drill string for selective movement betweenextended and contracted positions. Piston and chamber members arecooperatively arranged between the telescoping members for defining avariablevolume sample chamber having a minimum volume when thetelescoping members are in one of their positions and a maximum volumewhenever these members are moved to their other position. Valve meansare cooperatively arranged for admitting only a predetermined volume ofdrilling mud into the sample chamber in response to a predeterminedmovement of the telescoping members so that, upon movement of thetelescoping members toward their other position, the volume of thesample chamber will be sufficiently expanded to insure that the pressureof the entrapped mud sample will be reduced to at least the saturationpressure of a gas-containing mud sample at ambient boreholetemperatures. In this manner, when the apparatus of the presentinvention is coupled in a drill string, measurements of the forceapplied to the drill string for accomplishing the expansion of thesampling chamber will enable determinations to be readily made at thesurface as to whether or not the drilling mud sample is free ofentrained formation gas.

.vention, together with further objects and advantages thereof, may bebest understood by way of the following description of exemplaryapparatus employing the principles of the invention as illustrated inthe accompanying drawings, in which:

FIG. 1 schematically illustrates a portion of typical rotary drillingrig and its associated equipment and drill string along with oneembodiment of apparatus arranged in accordance with the presentinvention;

FIG. 2 is an enlarged cross-sectional view of the embodiment of thepresent invention shown in FIG. 1;

FIGS. 3A-3C successively depict various positions of the apparatusillustrated in FIG. 2 when it is being operated;

FIGS. 4A-4D graphically represent certain principles of the operation ofthe apparatus of the present invention;

FIG. 5A is a view similar to FIG. 2 but showing an alternativeembodiment of apparatus arranged in accordance with the principles ofthe present invention;

FIG. 5B depicts the apparatus of FIG. 5A as it is being operated;

FIGS. 6A and 6B are successive, enlarged crosssectional views of anotherpreferred embodiment of apparatus of the present invention;

FIGS. 7A and 7B schematically depict successive positions of theapparatus illustrated in FIGS. 6A and 68 during its operation; and

FIGS. 8A-8B graphically represent the operational principles of theapparatus of the present invention depicted in FIGS. 6A and 6B.

Turning now to FIG. 1, a new and improved testing tool 10 arranged inaccordance with the present invention is depicted as being tandemlycoupled in a typical drill string 11 comprised of a plurality of jointsof drill pipe 12, one or more drill collars 13, and a rotary drillingbit 14. As is customary, the drilling operation is accomplished by meansof a typical drilling rig 15 which is suitably arranged for drilling aborehole 16 through various earth formations, as at 17, until a desireddepth is reached. To accomplish this, the drilling rig 15 conventionallyincludes a drilling platform 18 carrying a derrick 19 which supportsconventional cable-hoisting machinery (not shown) suitably arranged forsupporting a hook 20 which is coupled thereto by means of aweight-measuring device 21 having an indicator or recorder 22 arrangedtherewith. As is customary, the

hoisting hook 20 supports a so-called swivel 23 and a tubular kelly 24which is coupled in the drill string 1 1 to the uppermost joint of thedrill pipe 12 and is rotatively driven by a rotary table 25 operativelyarranged on the rig floor 18. The borehole 16 is filled with a supply ofdrilling mud 26 for maintaining pressure control of the various earthformations, as at 17; and the drilling mud is continuously circulatedbetween the surface and the bottom of the borehole during the course ofthe drilling operation for cooling the drill bit 14 as well as forcarrying away earth cuttings as they are removed by the drill bit. Tocirculate the drilling mud 26, the drilling rig 15 is provided with aconventional mud-circulating system including one or more high-pressurecirculating pumps (not shown) that are coupled to the kelly 24 and thedrill pipe 12 by means of a flexible hose 27 connected to the swivel 23.As is typical, the drilling mud 26 is returned to the surface throughthe annulus in the borehole 16 around the drill string 1 l anddischarged via a discharge conduit 28 into a so-called mud pit" (notshown) from which the mud-circulating pumps take suction.

Turning now to FIG. 2, an enlarged cross-sectional view is depicted ofthe upper portion of the well tool 10. As seen there, the new andimproved testing tool 10 includes an elongated tubular mandrel 29 whichis coaxially arranged in an elongated tubular body 30 and adapted forlongitudinal movement in relation thereto between the contractedposition illustrated and a fullyextended position. To define thelongitudinal positions of the telescoping members relative to oneanother, an inwardly-opening recess 31 is provided within the axial bore32 of the body 30 and adapted for receiving an enlarged-diametershoulder 33 on the mandrel 29. It will be appreciated, therefore, thatthe extent of the longitudinal travel of the telescoping members 29 and30 is determined by the longitudinal spacings between the mandrelshoulder 33 and the opposed body shoulders which are respectivelydefined by the upper and lower surfaces 34 and 35 of the enlarged recess31. One or more inwardly projecting splines 36 are cooperativelyarranged on the body 30 and slidably received within complementaryelongated grooves 37 formed longitudinally along the exterior of themandrel 29 for corotatively securing the telescoping members to oneanother. In this manner, the telescoping members 29 and 30 areco-rotatively secured to one another for transmitting the rotation ofthe drill pipe 12 through the testing tool 10 to the drill collars l3and the drill bit 14 therebelow.

To couple the tool 10 into the drill string 1 1, a socket is formed inthe upper end of the mandrel 29 and appropriately threaded, as at 38,for threaded engagement with the lower end of the next adjacent joint ofthe drill pipe 12. Although the lower portion of the tool 38 is notillustrated in FIG. 2, it will be appreciated that the lower end of thebody 30 is either similarly arranged or provided with male threadsadapted for threaded engagement within a complementary threaded socketon the upper end of the next-adjacent drill collar as at 13. In thepreferred embodiment of the well tool 10, a fluid seal 39 is provided onthe enlarged mandrel shoulder 33 for sealing engagement with the innerwall of the recess 31 and one or more wipers 40 are arranged around theupper end of the body 30 to remove accumulations of mud and'the likefrom the spline grooves 37 and the exterior of the mandrel 29.

Of particular significance to the present invention, the new andimproved testing tool 10 further includes one or more similar oridentical fluid-sampling devices, as at 41, which are cooperativelyarranged between the telescoping members 29 and 30 for selectiveoperation upon longitudinal movements of the members in relation to oneanother. In the preferred embodiment of the testing tool 10 shown inFIG. 2, each of the sampling devices 41 includes an elongated body 42having a longitudinal bore formed in its upper portion and defining achamber 43 in which an elongated piston 44 is telescopically arrangedand adapted for sliding movement relative to the body between thecontracted position illustrated and one or more extended positions to besubsequently described. Sealing means, such as a suitable O-ring 45cooperatively arranged near the upper end of the piston chamber 43, areprovided for fluidly sealing the piston 44 in relation to the body 42.The lower portion of the body 42 is cooperatively arranged to provide anenlarged chamber 46 which is separated from the piston chamber 43 by aninwardlydirected annular shoulder having its lower face suitably shaped,as at 47, for defining an annular valve seat adapted for complementallyreceiving a valve member 48 which is movably disposed in the enlargedchamber. Biasing means, such as a relative weak compression spring 49,are cooperatively arranged in the chamber 46 between the body 42 and thevalve member 48 for normally maintaining the valve member in seatingengagement with the valve seat 47. One or more lateral ports, as at 50,are arranged in the body 42 to provide fluid communication between theborehole 16 and the enlarged chamber 46.

For reasons that will subsequently become apparent, the piston member 44is cooperatively arranged to provide an axial bore 51 therein which hasa venting passage 52 at its upper end and receives an elongated rod 53that is slidably disposed therein and extended downwardly therefromthrough a reduced-diameter annular shoulder 54 at the lower end of thebore. Biasing means, such as a moderately-strong spring 55 positioned inthe axial bore 51 between the upper end of the piston member 44 and anenlarged head 56 on the rod 53, are cooperatively arranged for normallyurging the rod downwardly through the valve seat 47 and into engagementwith the opposed face of the valve member 48. Thus, as depicted in FIG.2, so long as the piston 44 remains in its fully-contracted position inrelation to the body 42,,the stronger biasing spring 55 will extend therod 53 through the valve seat 47 and urge the rod tip against the valvemember 48 for maintaining it out of seating engagement with the valveseat.

In the preferred manner of coupling one or more of the sampling devices41 to the tool 10, the upper and lower ends of the piston 44 and theelongated body 42 are respectively secured to the telescoping members 29and 30 by means such as hooks 57 and 58 which are releasably coupled totransversely positioned pins 59 and 60 on the telescoping membersrespectively. Springloaded detents, as at 61, are arranged for retainingthe hooks 57 and 58 on their respective pins 59 and 60. To minimize theoverall exterior diameter of the tool 10, it is preferred to formappropriately shaped longitudinal recesses, as at 62 and 63, in thetelescoping members 29 and 30 so that once the sampling devices 41 arereleasably secured thereto, they will be substantially or entirelyconfined within the exterior circumference of the tool to reduce thelikelihood that the sampling devices might be damaged as the tool isbeing operated in the borehole 16.

Turning now to FIGS. 3A-3C, successive schematic views are shown of thewell tool during the course of a testing operation, with greatlyenlarged views being shown in each figure of one of the fluid samplingdevices 41 as these elements will appear while a test is being made inaccordance with the methods of the invention as described in the parentapplications of the present application to determine whether or not gasis then present in the drilling mud 26. As depicted in FIG. 3A, thetelescoping members 29 and of the new and improved tool 10 are initiallyfully contracted in relation to one another and the body 42 and thepiston 44 of the fluid-sampling device 41 will likewise be in theirfully contracted positions in relation to one another. so long as thepiston member 44 is fully retracted within the body 42, the spring 55will be effective for urging the rod 53 downwardly against the valvemember 48. Since the spring 55 is somewhat stronger than the spring 49,the net effect will be for the rod 53 to maintain the valve member 48spatially disposed below and out of contact with the valve seat 47.Thus, the drilling mud 26 in the borehole 16 immediately exterior of thefluid-sampling device 41 will be free to enter the chamber 46 by way ofthe ports to fill the lowermost portion of the elongated bore 43 belowthe piston 44. It will be recognized, of course, that by virtue of theventing passage 52, there are no unequal pressure forces acting on thesampling device 41 and the piston 44 will remain fully retracted. Thespring will be effective for urging the rod 53 downwardly to maintainthe valve member 48 open against the counteracting closing force of thespring 49.

It will be appreciated that if the drill string 11 is elevated, themandrel 29 will be free to travel upwardly relative to thelongitudinally stationary body 30 until the shoulder 33 engages theshoulder 34. Conversely, if the drill string 11 is maintained at thesame vertical or longitudinal position in relation to the borehole 16while the drill string is being rotated, as the drill bit 14progressively cuts away the formation materials in contact therewith theweight of the drill collars 13 will carry the body 30 downwardly inrelation to the longitudinally stationary mandrel 29 until such timethat the shoulder 33 contacts the shoulder 34. Thus, in either event,the net effect will be to progressively move the telescoped members 29and 30 as well as the body 42 and the piston 44 from their respectiveretracted positions illustrated in FIG. 3A toward their respectivemore-extended positions illustrated in FIG. 3B.

It will be appreciated, therefore, that upon expansion of the free spacewithin the axial bore 43 as the piston member 44 moves upwardly inrelation to the elongated body 42, the piston member will induct adiscrete volume of the mud-26 into the sampling device 41. As will benoted by comparison of FIGS. 3A and 3B, it will be recognized that thevalve member 48 will remain disengaged from the valve seat 47 until suchtime that the inwardly directed shoulder 54 in the elongated piston 44comes into contact with the enlarged head 56 on the upper end of the rod53. Thus, as shown in FIG. 3B, once the shoulder 54 engages the enlargedhead 56, the spring 55 is no longer effective for urging the rod 53downwardly so that further upward movement of the piston 44in relationto the body 42 will disengage the tip of the rod from the valve member48 so that thespring 49 will then urge the valve member into seatingengagement with the valve seat 47. Once this occurs, therefore, it willbe recognized that a discrete volume of the drilling mud 26 will then beentrapped within the free portion of the axial bore 43 as defined atthat time between the lower end of the piston 44 and the valve seat 47.Accordingly, it will be recognized that any further upward movement ofthe piston member 44 in relation to the body 42 must result in areduction of the pressure of the entrapped sample of the drilling mud 26before the tool 10 can assume the position illustrated in FIG. 3C.

To understand the operation of the apparatus of the present invention,it must be recognized that the physical characteristics of the mudsample entrapped in the piston chamber 43 will determine the sequence ofevents upon further upward movement of the mandrel 29 and the pistonmember 44. First of all, those skilled in the art will appreciate thatif only a gas were entrapped in the piston chamber 43, further upwardtravel of the piston member 44 from its intermediate position shown inFIG. 3B toward its fully-extended position depicted in FIG. 3C wouldsimply cause the gas to expand accordingly. Thus, in this unlikelysituation, there would be no significant forces restraining upwardtravel of the mandrel 29 and the piston 44 which is coupled thereto. Thepressure of the entrapped gas sample would merely be reduced in keepingwith the general gas laws.

As a result, an observer at the surface viewing the weight indicator 22will note a steady increase in the measured reading as upward movementof the drill string 11 progressively picks up the weight of the drillpipe 12 and the mandrel 29. Once the shoulder 33 is disengaged from theshoulder 35, the weight indicator 22 will show the entire weight of thekelly 24, the drill pipe 12, and the mandrel 29. This reading will, ofcourse, remain unchanged until the shoulder 33 engages the shoulder 34.From that point on, continued upward movement of the drill string 11will produce a continued increase in the reading shown on the indicator22 until the drill bit 14 is picked up from the bottom of the borehole16. The total reading shown on the weight indicator 22 will, of course,then be the full weight on the entire drill string 11.

As shown in FIG. 4A, the readings, W, of the weight indicator 22 in thisparticular situation when plotted against the upward travel, D, of thedrill string 11 will be generally as graphically represented by thecurve 64. These readings will, therefore, first follow an ascendingsloping line, as at 65, until the shoulder 33 is first disengaged fromthe shoulder 35. The indicated weight, W, will then, as indicated at 66,remain constant over that portion of the tool stroke (1,, where theshoulder 33 is moving away from the shoulder 35 and until the valvemember 48 is seated on the valve seat 47 (FIG. 3B). As previouslymentioned, even when a gas is trapped in the piston chamber 43 byclosure of the valve member 48, the remaining travel d of thepiston 44will be without significant restraint so that the reading on the weightindicator 22 will remain substantially unchanged (as graphicallyrepresented at 67 in FIG. 4A) until the shoulder 33 engages the shoulder34.

Thereafter, as graphically represented at 68, further upward travel, D,of the drill pipe 12 will again produce an increasing reading, W, on theweight indicator 22 as the weight of the drill collars 13 isprogressively added to that of the drill pipe already supported by thehook 20.

Accordingly, it will be recognized that if only a purely gaseous sampleis trapped in the piston chamber 43, the readings on the weightindicator 22 will generally be as represented by the curve 64 in FIG.4A. The abrupt changes, as at 69 and 70, in the slope of the curve 64will clearly define the points during the operation of the new andimproved tool when the shoulder 33 is respectively disengaging from theshoulder 35 and engaging the shoulder 34. Those skilled in the art willappreciate, therefore, that readings such as those just described willbe readily apparent at the surface since the respective weights of thedrill pipe 12 on the one hand and those of the drill collars l3 and thedrill bit 14 on the other hand are always known with a fair degree ofaccuracy.

The situation just described will, of course, be significantly differentwhere closure of the valve member 48 traps a sample in the pistonchamber 43 that is entirely a liquid. If this is the case, continuedupward travel of the drill pipe 12 will simply be incapable of producingfurther extension of the piston 44 in relation to the body 42 until orunless the forces tending to pull the piston and the body apart aresufficient to reduce the pressure of the entrapped liquid sample to itssaturation pressure at the existing ambient borehole temperature.

This will, of course, induce flashing of the entrapped liquid sample. Inthis event, once flashing of the liquid sample commences, the piston 44will then be free to move upwardly toward its extended position untilthe shoulder 33 engages the shoulder 34.

As shown in FIG. 48, therefore, the reading, W, on the indicator 22 willgenerally vary as represented by the graph 71 where the entrapped sampleis initially completely liquid but is ultimately reduced to itssaturation pressure at the ambient borehole temperature. Initial upwardmovement of the piston 44 toward its intermediate position (FIG. 33)will again cause a steady increase in the reading, W, on the weightindicator 22 until the shoulder 33 disengages from the shoulder 35 (thepoint 72 on the curve 71). Then, there will be no further increase inweight (as shown by the line segment 73) until the valve 48 is seated onits associated seat 47 (the point 74 on the curve 71 Further upwardtravel, D, of the drill pipe 12 will then produce a second steadyincrease of observed weight as shown at 75 on the curve 71.

Once the forces tending to separate the piston 44 and the body 42 aresufficient to reduce the pressure of the entrapped liquid sample to itssaturation pressure at the ambient temperature and flashing of thesample is commenced, as shown at 76 in FIG. 4B there will be nosignificant increase in the reading on the weight indicator 22 until theshoulders 33 and 34 are engaged to begin imposing the combined weight onthe drill collars l3 and the bit 14 onto the hook 20. This will thencause an increasing reading, W, on the indicator as shown at 77.

The third situation that may occur is where a wholly liquid sample istrapped in the piston chamber 43 but the forces tending to separate thepiston 44 and the body 42 are insufficient to induce flashing of thetrapped liquid sample. It will be appreciated that this can occur where,for a given size of the piston, there is an insufficient number of drillcollars 13 in the drill string 11 below the tool 10 to impose asufficient downward force on the tool for allowing the piston 44 to befully extended. Thus, the combined weight of the drill collars 13 andthe drill bit 14 is a limiting factor for determining whether acompletely-liquid sample will be flashed in the chamber 43 during theoperation of the tool 10 of the present invention. As shown in FIG. 4C,therefore, this situation is graphically represented at 78. It will berecognized that the curve 78 is similar to the left-hand portion of thecurve 71 in FIG. 48 so further explanation is believed unnecessary. Itshould be noted, of course, that the shoulder 33 will not engage theshoulder 34 so that extension of the tool 10 will be halted just afterthe valve member 48 is closed.

The situation graphically illustrated in FIG. 4D is where a liquid mudsample has only a small percentage of entrained gas. This is, of course,what should usually be expected where a high-pressure gas is initiallyentering the borehole l6 and a blowout is possibly commencing. As shownin FIG. 4D by the curve 79, the initial operation of the new andimproved tool 10 will be similar to the previously described situations.Once, however, the valve 48 is seated, as at 80 on the curve 79, thecontinued upward travel of the drill pipe 12 will induce movement of thepiston 44 toward its fully extended position with substantially lessforce being required than where the entrapped sample is wholly liquid.This will be readily understood when it is realized that the presence ofentrained gas in an entrapped liquid sample will make the saturationpressure of the mixture correspondingly higher than that of a purelyliquid sample. Thus, less force is required to fully extend thetelescoping members 29 and 30 and the body 42 and the piston 44. This isgraphically represented by the curved segment 81 of the curve 79.

Accordingly, it will be recognized by considering FIGS. 4A-4D that therelationship of the force applied for elevating the drill pipe 12 tofully extend the telescoping members 29 and 30 will be wholly dependentupon the physical state of the sample which is entrapped in the pistonchamber 43 upon closure of the valve member 48. Thus, as shown in FIG.4A, if the entrapped sample is purely gas, there will be no significantincrease in the force required to move the telescoping members 29 and 30from their fully contracted position to their fully extended position.On the other hand, FIGS. 4B and 4C demonstrate that if the entrappedsample is solely a liquid, once the valve member 48 has been seatedthere will be a significant and readily recognizable increase in theforce required to move the telescoping members 29 and 30 to theirfullyextended position-if such is ever reached. As graphicallyrepresented in FIG. 4D, however, the presence of even a small percentageof gas which may be entrapped in an otherwise wholly-liquid sample willproduce only a slowly ascending increase of the weight reading, W, onthe indicator 22. Accordingly, it will be recognized that in any of thefour above-described situations, observing the readings, W, of theweight indicator 22 in conjunction with the upward travel, D, of theexposed end of the drill pipe 12 will providea readily detectablesurface indication of the state of the drilling mud 26 which is thenadjacent to the testing tool 10 of the present invention.

The preceding descriptions have assumed that the testing operations wereconducted by elevating the drill pipe 12 in relation to the drillingplatform 18. It will be appreciated, however, that identical reactionswill be obtained where the drill pipe 12 is maintained at about the samelongitudinal position as the drill string 11 is being rotated. If thisis the situation, it will be recognized that as the drill bit 14continues to cut away at the bottom of the borehole 16, the weight ofthe drill collars 13 and the drill bit will tend to carry the bodies 30and 42 downwardly in relation to the longitudinally stationary mandrel29 and the piston member 44. Thus, the same results as previouslydescribed will be obtained.

In other words, downward movement of the drill bit 14 will progressivelycarry the body 42 downwardly in relation to the longitudinallystationary piston member 44 so that the valve member 48 will ultimatelybe closed once the enlarged rod head 56 engages the shoulder 54.Thereafter, the weight reading, W, which will be registered by theindicator 22 will again be determined by the nature or state of theentrapped fluid within the piston chamber 43. Stated another way, sincethe combined weight of the drill collars 13 and v the drill bit 14represent the maximum force which can be effective for moving thetesting tool 10 to its fully extended position, the above detaileddescriptions are equally applicable regardless of whether it is theupper member'29, and 44 which are being moved upwardly in relation tothelongitudinally stationary lower members 30 and 42or it is the lowermembers which are being moved downwardly in relation to thelongitudinally stationary upper members. In either case, easilyrecognized surface indications will be provided to warn the observer ofan impending blowout.

Turning now to FIG. 5A, an enlarged cross-sectional view is shown of theupper portion of another testing tool 100 which is also arranged inaccordance with the principles of the present invention. The testingtool 100 includes an elongated tubular member 101 which is coaxiallydisposed within an elongated tubular body 102 and suitably arranged forlongitudinal movement in relation thereto between the depicted retractedposition and a fully extended position. It will, of course, be recand102 are co-rotatively secured to one another as by one or more sets ofmating splines and grooves as at 103 and 104. Similarly, anenlarged-diameter shoulder 105 on the mandrel 101 is cooperativelyarranged within a recess 106 provided within the total body 102 forestablishing the contracted and extended positions of the telescopingmembers. Other similar details will be noted.

The significant difference between the tool 10 and the tool 100 is,however, that the latter tool has an integral fluid-sampling deviceshown generally at 107 which is cooperatively arranged between thetelescoping members 101 and 102 for operation in a similar fashion tothe first-described testing tool. In the preferred embodiment of thetesting tool 100 shown in FIG. 5A, the sampling device 107 is providedby arranging a piston chamber 108 in the upper end of the body 102 whichreceives an enlarged-diameter portion 109 of the mandrel 101 having afluid seal 110 operatively disposed therearound. In this manner, uponupward movement of the mandrel 101 in relation to the body 102, the freespace in the piston chamber 108 will be expanded in a similar manner asthe sampling devices 41.

To accomplish the necessary valving action such as previously describedin relation to the sampling devices 41, that portion of the mandrel 101immediately below the enlarged-diameter piston member 109 is reduced indiameter, as at 111, and the next immediately adjacent portion of themandrel is enlarged in diameter, as at 112, to provide a valve member.In this manner, on the initial upward movement of the mandrel 101, theexpansion of the piston chamber 108 will induce a flow of the drillingmud 26 through one or more lateral ports 113 arranged in the body 102below an inwardly facing seal 114 which is mounted in the interior bore115 of the body to provide a valve seat for the enlargement 1 12. Thus,drilling mud will be drawn into the progres sively enlarged pistonchamber 108 until the enlargeddiameter portion 112 of the mandrel 101first engages the sealing member 114. At this point, a discrete sampleof the drilling mud 26 will be entrapped within the piston chamber 108so that further upward travel of the mandrel 101 in relation to the body102 will produce the same variations on the weight indicator 22 as thosepreviously described with reference to FIGS. 4A-4D.

From the foregoing descriptions of the new and improved testing tools 10and 100, it will be appreciated from FIGS. 4A-4D that an observer at thesurface can readily deduce from the changes in the weight readings, W,on the indicator 22 in association with upward. movement of the drillstring 11 whetheror not gas is then present in the borehole 16 in thevicinity of the drill collars 13. Thus, a simple go-no go type of testcan be readily performed during the course of the drilling operationmerely by elevating the drill string 11 a sufficient distance to fullyextend the telescoping members of the testing tool 10 (or 100) andobserving the resulting effects as visibly displayed on the weightindicator 22. A test of this nature can, of course, be rapidly conductedwith no appreciable interruption of the drilling operation. Moreover, ifnecessary, several tests can be conducted for verification by simplylowering the drill string 11 to expel the first sample and repositionthe various elements of the testing tool (or 100).

It should be noted that the new and improved testing tools 10 and 100are also capable of operation without raising the drill string 11. Thus,at any time during a drilling operation, if the drill string 11 isslacked off to be certain that the telescoping members of the testingtool 10 (or 100) are in their respective fully telescoped positions, asthe drilling operation commences the drill bit 14 will progressivelydeepen the borehole 16 to move the telescoping members toward theirextended positions. An observer can, therefore, note the time intervalrequired for the telescoped members of the testing tool 10 (or 100) tomove to the point where the valve member 48 is first seated (or theenlarged portion 112 is first sealingly engaged with the seal 114). Thistime interval can, of course, be readily determined at the surface sincethe pronounced cessation of the increasing weight indications whichoccurs once the full weight of the drill pipe 12 is suspended on thehook 20 will identify when the telescoping members first start movingand the next change in the weight indication will show when the valvemember is first seated.

Once it is known how long ittakes for the valve member of the testingtool 10 (or 100) to be closed, it can be safely assumed that the sametime interval will be required for the telescoping members to move totheir fully-extended positions since the valve closes at the mid-pointof the stroke of the tool. A proportional relationship will, of course,always exist between the times required and d, and d irrespective of theactual point in the stroke of the telescoping members that the valvemember is seated. Accordingly, by observing the variations in theindicated weight, W, during this second time interval, an observer canreliably deduce whether gas is then present in the borehole 16 adjacentto the drill collars 13. I-Iereagain, if during drilling an indicationis routinely obtained that gas is or may be present, it is quite easy tolower the drill pipe 12 to expel the mud sample then in the testing tool10 (or 100) and then either continue drilling or else elevate the drillpipe to make a second test for verifying the first test.

It has been found, however, that the new and improved apparatus of thepresent invention can also be employed for quantitatively measuring witha fair amount of precision the amount of gas entering the borehole 16during the course of the drilling operation. As previously described,the various dimensions of the testing tools 10 and 100 are, of course,known. Thus, by measuring the additional force, AW, required to extendthe piston 44 (or 109) from just after the point that the fluid samplehas been entrapped to the point where the piston is fully extended, aunique relationship between this force and the tool displacement, d isdetermined by the percentages of gas if any which is then entrained inthe entrapped sample. As previously described with reference to FIGS. 4Band 4C, if the entrapped sample is wholly liquid, the rapid changes inthe indicated weight, W, on the indicator 22 through the stroke, d ofthe piston member 44 (or 109) within the piston chamber 43 (or 108) willpro-' vide a positive indication at the surface that the entrappedsample is wholly free of any entrained gas. Conversely, the forcerequired for moving the piston member 44 (or 109) to its fully extendedposition will be directly related to the percentage of gas which is thenentrained in the entrapped fluid sample. This unique relationship isexpressed by the equation:

Percent gas (by volume) (d /d ){[(P,,XA)/(W2- 1) ]l}X percent where,

d longitudinal displacement of the telescoping members required toinduct a sample of mud into the piston chamber; d maximum longitudinaldisplacement of the telescoping members between the point where thevalveis closed to the point where the telescoping members are fully extended;

P,, hydrostatic pressure of the drilling mud at the depth at which thesample is being taken;

A cross-sectional area of the piston(s);

W weight indication at the time a sample is being inducted into thepiston chamber; and

W weight indication when the telescoping members are first fullyextended.

It should also be understood that once the sample is trapped in thepiston chamber 43 (or 108), the force being indicated on the weightindicator 22 at any given point during the continued movement of thetelescoping members 29 and 30 (or 101 and 102) will be directly relatedto the amount of entrained gas in the sample. This relationship is bestexpressed by the following equation:

Percent gas (by volume) (Ad/d )[(W -W)/W] IOO percent where,

Ad longitudinal displacement of the telescoping members between thepoint where the valve is closed to the point where the measurementis'being made;

d maximum longitudinal displacement of the telescoping members betweenthe point where the valve is closed to the point where the telescopingmembers are fully extended;

W weight indication at the time the measurement is being taken less theweight of the drill pipe or drill string above the tool. This latterweight must be corrected to account for the buoyancy of the drill pipeor drill string in the particular drilling mud being used; and

W the product of depth, mud density, and the area of the samplingpiston(s).

Turning now to FIGS. 6A-6B, successive enlarged cross-sectional viewsare depicted of another well tool 200 which also incorporates theprinciples of the present invention. As seen there, the new and improvedtesting tool 200 includes an elongated tubular mandrel 201 which iscoaxially arranged in an elongated tubular body 202 and adapted forlongitudinal movement in relation thereto between the contractedposition illustrated in FIGS. 6A and 6B, a first intermediate positionas schematically shown in FIG. 7A, a second intermediate position justabove the first, and a fully extended position as depicted in FIG. 7B.The body 202 is reduced slightly, as at 203, and provided with one ormore elongated longitudinal grooves cooperatively arranged to slidablyreceive a corresponding number of outwardly projecting splines 204 onthe mandrel 201 for co-rotatively securing the telescoping members toone another (FIG. 6A). In this manner, when the tool 200 is substitutedfor the tool 10 shown in FIG. 1, the telescoping members 201 and 202 areco-rotatively secured to one another for transmitting the rotation ofthe drill pipe 12 through the testing tool 200 to the drill collars 13and the drill bit 14 therebelow. Opposed shoulders 205 and 206 at thelower ends of the splines 204 and the reduced body portion 203 definethe upper limit of telescopic movement of the telescoping members 201and 202 relative to one another. It will also be appreciated that theopposed shoulders 207 and 208 provided by the upper ends of the mandrel201 and the body 202, respectively, will cooperate to define the lower.travel limit or fully contracted position of these two telescopingmembers.

To couple the tool 200 into the drill string 11, a socket is formed inthe upper end of the mandrel 201 and appropriately threaded, as at 209,for threaded engagementwith the lower end of the next adjacent joint ofdrill pipe 12. The lower end of the body 202 is either similarlyarranged or provided with male threads, as at 210, adapted for threadedengagement within a complementary threaded socket on the upper end ofthe next-adjacent drill collar as at 13. In the preferred em bodiment ofthe well tool 200, a fluid seal 211 is mounted within the lower end ofthe body 202 for sealing engagement with the lowermost portion of themandrel 201; and one or more wipers 212 are arranged around the upperend of the body to remove accumulations of mud and the like from thesplines 204 and the exterior of the mandrel.

The new and improved tool 200 is further arranged to define anexpansible fluid-sampling chamber 213 between the inner and outermembers201 and 202, with the upper and lower limits of the chamber beingdetermined by spaced, internally reduced portions 214 and 215 in theaxial bore 216 of the body. Fluid ports 217 and 218 are arranged in thebody 202 above and below the seats 214 and 215 respectively to providefluid communication between the axial bore 216 and the borehole l6exterior of the tool 200.

The mandrel l'is cooperatively arranged to include piston means, such asan enlarged piston member 219 having sealing members such as one or morechevron seals 220 mounted thereon, adapted for inducting drilling mudfrom the borehole 16 into the sampling chamber 213 as the mandrel ismoved upwardly in relation to the body 202 between its retractedposition shown in FIGS. 6A and 6B and the first intermediate positionschematically depicted in FIG. 7A. The mandrel 201 is also arranged toinclude valve means such as an enlarged valve member 221 spaced belowthe piston member 219 and carrying sealing members such as 'one or moredownwardly directed chevron seals 222.

As will subsequently be explained in greater detail, the seals 220 and222 and the reduced bore portions 214 and 215 are cooperatively spacedso that once the mandrel 201 is in the intermediate position shown inFIG. 7A, the upper and lower seals will be sealingly engaged with theupper and lower reduced portions, respectively, to fluidly seal anentrapped mud sample in the chamber 213.

It will be appreciated from FIG. 7A, that during that part of the travelof the mandrel 201 in relation to the body 202 from the firstintermediate position where the upper seals 220 first sealingly engagethe upper reduced bore portion to the second intermediate position wherethe upper seals are no longer sealingly engaged with this bore portion,the volume of the sample chamber 213 will be increased in proportion tothe difference in diameter of the upper and lower bore portions 214 and215. Stated another way, as the mandrel 201 moves upwardly between theaforementioned intermeof the chamber 213 will, therefore, be limited tothat which will be obtained as the mandrel 201 moves over the shortdistance where the seals 220 and 222 are both respectively engaged withthe upper and lower bore portions 214 and 215. Thus, the sample chamber213 will be expanded only as the mandrel 201 is moved between the twointermediate positions which occur only so long as both the upper andlower seals 220 and 222 are simultaneously sealingly engaged with theirrespective sealing surfaces 214 and 215. As seen in FIGS. 6A and 6B, thelongitudinal spacing between these two intermediate positions of theinner and outer members 201 and 202 will, in general, be determined bythe axial heights of the seals 220 and 222 as well as of thereduced-bore portions 214 and 215.

Once the mandrel 201 is moved further upwardly, however, the chamber 213will be re-opened whenever one of the two seals 220 and 222 is no longersealingly engaged with its associated sealing surface 214 and 215. Thus,it will be appreciated that in the operation of the new and improvedtool 200, the piston 219 will ultimately be moved upwardly above thesample chamber 213 to release the sample from the chamber as the mandrel201 is moved toward the fully extended position of the tool 200 asdefined by the abutment of the shoulders 205 and 206 and depicted inFIG. 7B.

It will be appreciated that if the drill string 11 is elevated, themandrel 201 will be free to travel upwardly relative to thelongitudinally stationary body 202 until the shoulder 205 engages theshoulder 206. Conversely, if the drill string 11 is maintained at thesame vertical or longitudinal position in relation to the borehole 16while the drill string is being rotated, as the drill bit 14progressively cuts away the formationmaterials in contact therewith theweight of the drill collars 13 will carry the body 202 downwardly inrelation to the longitudinally stationary mandrel 201 until such timethat the shoulder 206 contacts the shoulder 205. Thus, in either event,the net effect will be to progressively move the telescoped members 201and 202 as well as the piston 219 and the valve member 221 from theirrespective positions illustrated in FIGS. 6A and 6B toward theirrespective positions illustrated in FIG. 7A and 7B. 1

To determine whether or not gas is present in the drilling mud, thetelescoping members 201 and 202 of the new and improved tool 200 areinitially fully contracted in relation to one another so that the pistonmember 219 and the valve member 221 will be in their respectivepositions as depicted in FIGS. 6A and 68. So long as the piston member219 and the valve member 221 are in these positions, the drilling mud inthe borehole 16 immediately exterior of the fluid-sampling tool 200 willbe free to enter the sample chamber 213 by way of the ports 217 and 218to fill the enlarged bore 216 above the seal 211.

it will be appreciated, therefore, that upon expansion of the free spacewithin the axial bore 216 as the piston 219 moves upwardly in relationto the body 202, a discrete volume of the drilling mud and will beinducted into the sampling chamber 213. It should be noted that duringmovement of the mandrel 201 between the fully contracted position shownin FIGS. 6A and 6B and the first intermediate position shown in FIG. 7A,it is not essential that the seals 220 be engaged with the body 202since the piston 219 will readily displace drilling mud from the chamber213 by way of the ports 217 as fresh drilling mud is drawn into thesample chamber by way of the ports 218. As previously described withreference to FIG. 7A, the seals 222 on the valve member 221 will remaindisengaged from the valve seat 215 until such time that the seals 220 onthe piston member 219 are engaged with the upper seating surface 214.Once this occurs, as depicted in FIG. 7A, it will be recognized that adiscrete and known volume of the drilling mud will then be entrappedwithin the sample chamber 213 as defined at that time between the lowerpart of the piston member 219 and the upper part of the valve member221. Accordingly, any further upward movement of the mandrel 201 inrelation to the body 202 must first result in an expansion of the samplechamber 213 and, therefore, a corresponding reduction of the pressure ofthe entrapped sample of the drilling mud as the mandrel moves betweenits first and second intermediate positions.

To understand the principles of the operation of the new and improvedtool 200, it must be recognized that the physical characteristics of themud sample entrapped in the sample chamber 213 will determine thesequence of events upon further upward movement of the mandrel 201beyond the first intermediate position shown in FIG. 7A. First of all,those skilled in the art will appreciate that if only a gas wereentrapped in the sample chamber 213, further upward travel of themandrel 201 from its first intermediate position shown in FIG. 7A towardits second intermediate position would simply cause the entrapped gas toexpand accordingly. Thus, in this unlikely situation, there would be nosignificant forces restraining continued upward travel of the mandrel201. The pressure of the entrapped gas sample would merely be reduced inkeeping with the general gas laws as the mandrel 201 moves between itsfirst and second intermediate position. The mandrel 201 would, ofcourse, be easily moved to its fullyextended position as shown in FIG.7B.

The situation just described will, of course, be significantly difierentwhere seating of the piston member 219 and closure of the valve member221 traps a sample in the sample chamber 213 that is entirely a liquid.If this is the case, continued upward travel of the drill pipe 12 willsimply be incapable of producing further extension of the mandrel 201 inrelation to the body 202 beyond its first intermediate position unlessthe forces tending to fully extend the mandrel and the body aresufficient to reduce the pressure of the entrapped liquid sample in thechamber 213 to its saturation pressure at the existing ambient boreholetemperature. Thus, for reasons which will subsequently be explained, inthe preferred embodiment of the tool 200 the effective cross-sectionalareas of the piston member 219 and the valve member 221 are purposelyestablished to be certain that these forces are more than sufficient tofully extend the mandrel 201 in relation to the body 202.

As a result, in the operation of the tool 200 of the present invention,the presence of even a minor quantity of gas (e.g., something in theorder of 2-3 percent or more) in the drilling mud will be sufficient toenable the mandrel 201 to be moved in relation to the body 202 from itsfully contracted position to its fully extended position with a minimumdegree of restraint. On the other hand, the substantial or total absenceof gas in the drilling mud will result in an extreme force beingrequired to move the inner and outer members 201 and 202 from theircontracted position to their extended position.

To demonstrate that the degree of force required to extend thetelescoping members 201 and 202 will be directly related to the gascontent in the drilling mud, it has been found that the followingequation defines these forces:

Force (P XA) {l-(V,X percent Gas)/[(V,, percent Gas)+AV,,]}

where,

1 hydrostatic pressure of the drilling mud at the depth at which thesample is being taken;

A effective pressure area restraining movement of the telescopingmembers 201 and 202 to their fully extended position (cross-sectionalarea of the piston seat 214 less the cross-sectional area of the valveseat 215);

V volume of the sample chamber 213 when the tool 200 is positioned asshown in FIG. 6A;

Percent Gas percentage, by volume, of gas in the drilling mud; and

AV, increase in volume of the sample chamber 213 as the tool 200 isextended from the intermediate position shown in FIG. 6A to the nextintermediate position where the sample chamber is re-opened.

Accordingly, it will be seen from Equation 3 that for a givenarrangement of the tool 200 and hydrostatic pressure, when the gascontent in the drilling mud is zero, the force required to move thetelescoping members 201 and 202 so as to re-open the sample chamber 213will be directly related to the hydrostatic pressure, P,,, and theeffective pressure area, A, and, therefore, quite high. On the otherhand, since the volume, V,, of the sample chamber 213 is preferably muchlarger than the expansion volume, AV,, the bracketed fraction inEquation 3 will approach unity even with only minor percentages of gasin the drilling mud so that such minor amounts of gas will substantiallyreduce the force F. In the preferred arrangement of the new and improvedtool 200, the volume, V,, of the sample chamber 213 was selected to bein the order of times the expansion volume, AV, With typical hydrostaticpressures and an area, A, in the order of 3-sq. inches, the force, F,will be negligible whenever the gas content exceeds about 1-- 2 percent.

ditions to be experienced in operation of the tool 200 are graphicallydepicted. Taking the situation where there is a moderate to extremepercentage of gas in the drilling mud, an observer at the surfaceviewing the weight indicator 22 will note a steady increase in themeasured reading as upwardmovement of the drill string 11 progressivelypicks up the weight of the drill pipe 12 and the mandrel 201. Once theshoulder 207 is disengaged from the shoulder 208, the weight indicator22 will show the entire weight of the kelly 24, the drill pipe 12, andthe mandrel 201. This reading will, of course, remain substantiallyunchanged until the shoulder 205 engages the shoulder 206. From thatpoint on, continued upward movement of the drill string 11 will againproduce, a continued increase in the reading shown on the indicator 22until the drill bit 14 is picked up from the bottom of the borehole 16.The total reading shown on the weight indicator 22 will, of course,

then be the full weight of the entire drill string 11.

As shown in FIG. 8A, the readings, W, of the weight indicator 22 in thissituation when plotted against the upward travel, D, of the drill string1 1 will be generally as graphically represented by the curve 223. Thesereadings will, therefore, first follow an ascending sloping line, as at224, until the shoulder207 is first disengaged from the shoulder 208.The indicated weight, W, will then, as indicated at 225, remain constantover that portion of the tool stroke, d,, where the shoulder 207 ismoving away from the shoulder 208 and until the piston member 219 issealed within the reduced bore portion 214 and the valve member 221 isseated on the valve seat 215. As previously mentioned, when a gas istrapped in the sample chamber 213 by closure of the valve member 221,the short travel, d of the mandrel 201 between the two intermediatepositions will be without significant restraint so that the reading onthe weight indicator 22 will remain substantially unchanged (asgraphically represented at 226 in FIG. 8A) until the sample chamber 213is re-opened. Thereafter, as shown at 227, continued travel, d of themandrel 201 until it is halted (where the shoulder 205 engages theshoulder 206 will show an abrupt decrease as in the reading on theweight indicator 22. Once the total load on the hook 20 is reducedslightly to the weight of the kelly 24, the drill pipe 12 and themandrel 201, the reading, W, on the weight indicator 22 will againremain constant until the shoulders 205 and 206 are engaged as themandrel moves through the stroke, d;, between its second intermediateposition and its fullyextended position. As graphically representedat228, upon engagement of the shoulders 205 and 206, further upwardtravel, D, of the drill pipe 12 will again produce an increasingreading, W, on the weight indicator 22 as the weight of the drillcollars 13 is progressively added to that of the drill pipe alreadysupported by the hook 20.

Accordingly, it will be recognized that if a sample of gas-containingmud is trapped in the sample chamber 213, the readings on the weightindicator 22 will generally be as represented by the curve 223 in FIG.8A. The abrupt changes, as at 229 227 and 230, in the curve 223 willclearly define the respective points during the testing operation whenthe shoulder 207 is disengaging from the shoulder 208, when the samplechamber 213 is re-opened, and when the shoulder 205 is engaging theshoulder 206. Those skilled in the art will appreciate, therefore, thatreadings such as those just described will be readily apparent at thesurface since the respective weights of the drill pipe 12 on the onehand and those of the drill collars 13 and the drill bit 14 on the otherhand are always known with a fair degree of accuracy.

As previously explained by reference to Equation 3, the situation isreversed when there is no gas in the drilling mud. As described, themandrel will halt in its first intermediate position until the forceacting on the telescoping members 201 and 202 is sufficient to expandthe sample chamber 213. This will/of course, induce flashing of theentrapped liquid sample. In this event, once flashing of the liquidsample commences, the

mandrel 201 will then be free to move upwardly be-' yond its secondintermediate position and then toward its fully extended position wherethe shoulder 205 engages the shoulder 206.

As shown in FIG. 8B, therefore, the readings, W, on the indicator 22will generally vary as represented by the graph 231 where the entrappedsample is initially completely liquid but is ultimately reduced to itssaturation pressure at the ambient borehole temperatures. Initial upwardmovement of the mandrel 201 toward its first intermediate position (FIG.3) will again cause a steady increase in the reading, W, on the weightindicator 22 until the shoulder 207 disengages from the shoulder 208(the point 232 on the curve 231 Then,

there will be no further increase in weight (as shown by the linesegment 233) until the piston member 219 is sealed Within the bore 214and the valve member 221 is seated on its associated seat 215 (the point234 on the curve231). Further upward travel, D, of the drill pipe 12will then immediately produce a second steady increase of observedweight as shown at 235 on the curve 231.

Once the forces tending to further separate the mandrel 201 and the body202 are suffic'ient to reduce-the pressure of the entrapped liquidsample to its saturation pressure at the ambient temperature andflashing of the sample is commenced, as shown at 236 in FIG. 5, therewill be no significant increase in the reading on the weight indicator22 until the sample chamber 213 is reopened. I-lereagain, there will bean abrupt decrease, as at 237, in the reading, W, on the indicator 22and then a steady reading, as at 238, until the shoulders 205 and 206are engaged to begin imposing the combined weight of the drill collarsl3 and the bit 14 onto the hook 20. This will again cause an increasingreading, W, on the indicator as shown at 239.

It will be noted, however, that when the telescoping members 201 and 202move from their second extended position to their fully extendedposition, there will be a sudden impact (as represented by the surge inforce shown at 240 in FIG. 8B) as the shoulder 205 momentarily strikesthe shoulder 206. It will be recognized that this sudden shock or impactwill be caused by the momentary release of the forces tending to stretchthe drill pipe 12 as the telescoped members 201 and 202 are movedbetween their two intermediate positions. This impact will, of course,produce a sudden shock force similar to that imposed by a typicaldrilling jar. Those skilled in the art will appreciate that such impactsare easily detected at the surface. Accordingly, in the operation .ofthe new and improved tool 200, the absence of gas in the drilling mudwill produce a spaced succession of shocks or impacts which will signifythere is little or no gas in the drilling mud. On the other hand, shouldthese impacts cease, it will be known that gas entered the borehole l6and appropriate measures can be taken.

The preceding descriptions have assumed that the testing operations wereconducted by elevating the drill pipe 12 in relation to the drillingplatform 18. It will be appreciated, however, that identical reactionswill be obtained where the drill pipe 12 is maintained at about the samelongitudinal position as the drill string 11 is being rotated. If thisis the situation, it will be recognized that as the drill bit 14continues to cut away at the bottom of the borehole 16, the weight ofthe drill collars l3 and the drill bit will tend to carry the body 202downwardly in relation to the longitudinally stationary mandrel 201 andthe piston member 219 and the valve member 221. Thus, the same resultsas previously described will be obtained.

In other words, downward movement of the drill bit 14 will progressivelycarry the body 202 downwardly in relation to the longitudinallystationary piston member 219 and the valve member 221 so that the samplechamber 213 will ultimately be closed. Thereafter, the weight readings,W, which will be registered by the indicator 22 will again be determinedby the nature or state of the entrapped fluid within the sample chamber213. Stated another way, since the combined weight of the drill collarsl3 and the drill bit 14 represent the maximum force which can beeffective for moving the testing tool 200 to its fully extendedposition, the above detailed descriptions are equally applicableregardless of whether it is the mandrel 201 which is being movedupwardly in relation to the longitudinally stationary body 202 or it isthe body which is being moved downwardly in relation to thelongitudinally stationary mandrel. In either case, easily recognizedsurface indications will be provided to warn the observer of animpending blowout.

From the foregoing descriptions of the new and improved testing tool200, it will be appreciated from FIGS. 8A and 8B that an observer at thesurface can readily deduce from the changes in the weight readings, W,on the indicator 22 in association with upward movement of the drillstring 11 whether or not gas is then present in the borehole 16 in thevicinity of the drill collars 13. Thus, a simple go-no go type of testcan be readily performed during the course of the drilling operationmerely by elevating the drill string 11 a sufficient distance to fullyextend the telescoping members 201 and 202 of the testing tool 200 andobservingthe resulting effects as visibly displayed on the weightindicator 22. A test of this nature can, of course, be rapidly conductedwith no appreciable interruption of the drilling operation. Moreover, ifnecessary, several tests can be conducted for verification by simplylowering the drill string 1 l to expel the first sample and repositionthe various elements of the testing tool 200.

It should' be noted that the new and improved testing tool 200 is alsocapable of performing the abovedescribed test without raising the drillstring 11. Thus, at any time during a drilling operation, if the drillstring 11 is slacked off to be certain that the telescoping members 201and 202 of the testing tool 200 are in their respective fully telescopedpositions, as the drilling operation commences the drill bit 14 willprogressively deepen the borehole 16 to move the telescoping memberstoward their extended positions. An observer can, therefore, note thetime interval required for the telescoped members 201 and 202 of thetesting tool 200 to move to the point where the piston member 219 andthe valve member 221 is first seated. This time interval can, of co rse,be readily determined at the surface since the gi onounced cessation ofthe increasing weight indications which occurs once the full weight ofthe drill pipe 12 is suspended on the book 20 will identify when thetelescoping members 201 and 202 first start moving and the next changein the weight indication will show when the piston member 219 and thevalve member 221 are first seated.

It should be noted that the piston seals 220 are purposely oriented topreferably withstand a pressure differential acting downwardly.Similarly, the valve seals 222 are also oriented to preferably seal bestagainst a pressure differential acting upwardly. Thus, when the samplingchamber 213 is closed and the mandrel 201 is moved upwardly, the chamberwill be expanded to achieve a reduction in the pressure of the entrappedsample without leakage past the seals 220 and 222. Conversely, byorienting the seals 220 and 222 as depicted, downward movement of themandrel 201 will not tend to sealingly engage the seals with the body202. This will, of course, facilitate returning the telescoped members201 and 202 to their fully retracted position.

Accordingly, it will be appreciated that the present invention hasprovided new and improved apparatus for detecting the entry or presenceof gas in a borehole being excavated and signaling this to the surface.In the representative embodiments of the apparatus of the presentinvention disclosed herein, one or more unique sampling devices arearranged between the upper and lower telescoping members of a typicalslip joint which is tandemly connected in the drill string preferably ashort distance above the drill bit. Each of these fluid samplersincludes telescoping piston and chamber members defining an enclosedsample chamber which is expanded in response to extension of the slipjoint members. Valve means are cooperatively arranged with each of thesampling devices for admitting a predetermined volume of drilling mudinto the sample chambers each time the slip joint is extended.

In operating the tools of the present invention, they are connected intoa drill string and lowered into a borehole. Thereafter, a discretesample of drilling mud from the borehole is periodically trapped withinthe expansible sampling chamber defined between the telescoping members.By moving the drill string so as to expand the sampling chamber, thepressure of the entrapped sample is reduced to at least the saturationpressure of a gas-containing drilling mud at the borehole ambienttemperature. By measuring the force required to expand the samplingchamber, the presence or absence of formation gas in the drilling fluidcan be determined; and, if desired, these force measurements may be usedto derive quantitative measurements which are representative of thepercentage of gas entrained in the discrete sample.

While only particular embodiments of the present invention have beenshown and described, it is apparent that changes and modifications maybe made without departing from this invention in its broader aspects;and, therefore, the aim in the appended claims is to cover all suchchanges and modifications as fall within the true spirit and scope ofthis invention.

What is claimed is:

1. A well tool adapted for coupling into a drill string carrying a drillbit for excavating a borehole and cooperatively arranged for detectingwhether formation gas is contained in the drilling mud therein, saidwell tool comprising:

inner and outer tubular members telescopically arranged together forupward and downward movements relative to one another betweenlongitudinally spaced positions; and

fluid-sampling means operatively arranged between said telescopedmembers for defining an expansible fluid chamber adapted to be expandedfrom a reduced volume when said telescoped members are in one positionto a selected increased volume when said telescoped members are inanother position, passage means between said fluid chamber and theexterior of said fluid-sampling means, and valve means cooperativelyarranged on said fluidsampling means and selectively operable inresponse to relative movements between said telescoped members foradmitting drilling mud through said passage means as said fluid chamberis expanded from said reduced volume to a selected intermediate volumeand for blocking said passage means as said fluid chamber is expandedfrom said intermediate volume toward said increased volume for reducingthe pressure of a mud sample entrapped in said fluid chamber.

2. The well tool of claim 1 wherein said fluidsampling means include abody coupled to one of said telescoped members and having an internalbore, and a piston coupled to the other of said telescoped members andmovably disposed in said internal bore for defining said fluid chamber.

3. The well tool of claim 2 wherein said valve means include a valveseat defined in said passage means, a valve member movably disposed insaid passage means and cooperatively arranged for movement into and outof seating engagement with said valve seat, and actuating meansoperative upon relative movements between said body and said piston formoving said valve member into seating engagement with said valve seat assaid fluid chamber is expanded beyond said intermediate volume.

4. The well too] of claim 2 wherein said valve means include a valveseat defined in said passage means, a valve member movably disposed insaid passage means and cooperatively arranged for movement into and outof seating engagement with said valve seat, and actuating meansincluding first means normally biasing said valve member toward seatingengagement with said valve seat, an actuating member operativelyarranged on said piston for retaining said valve member out of seatingengagement with said valve seat until said body and piston arerelatively positioned where said fluid chamber is at its saidintermediate volume, and second means normally biasing said actuatingmember against said valve member until said body and piston arerelatively positioned where said fluid chamber has a volume equal to orgreater than said intermediate volume.

5 The well too] of claim 1 wherein said fluidsampling means includesealing means cooperatively arranged on said inner member andoperatively associated with the internal bore of said outer member fordefining said fluid chamber.

6. The well too] of claim 5 wherein said valve means include a fluidseal cooperatively arranged on one of said telescoped members in saidpassage means and a sealing surface cooperatively arranged on the otherof positions.

8. The well tool of Claim 1 wherein said means defining a fluid chamberinclude a longitudinal bore in said outer telescoped member havingenlarged-diameter and reduced-diameter portions, and a piston memberarranged on said inner telescoped member and disposed within saidlongitudinal bore for movement in said reduced bore portion uponmovement of said telescoped members from their said one position totheir said other position and for movement from said reduced boreportion into said enlarged bore portion upon movement of said telescopedmembers from their said other position to an extended position.

1. A well tool adapted for coupling into a drill string carrying a drillbit for excavating a borehole and cooperativelY arranged for detectingwhether formation gas is contained in the drilling mud therein, saidwell tool comprising: inner and outer tubular members telescopicallyarranged together for upward and downward movements relative to oneanother between longitudinally spaced positions; and fluid-samplingmeans operatively arranged between said telescoped members for definingan expansible fluid chamber adapted to be expanded from a reduced volumewhen said telescoped members are in one position to a selected increasedvolume when said telescoped members are in another position, passagemeans between said fluid chamber and the exterior of said fluid-samplingmeans, and valve means cooperatively arranged on said fluid-samplingmeans and selectively operable in response to relative movements betweensaid telescoped members for admitting drilling mud through said passagemeans as said fluid chamber is expanded from said reduced volume to aselected intermediate volume and for blocking said passage means as saidfluid chamber is expanded from said intermediate volume toward saidincreased volume for reducing the pressure of a mud sample entrapped insaid fluid chamber.
 2. The well tool of claim 1 wherein saidfluid-sampling means include a body coupled to one of said telescopedmembers and having an internal bore, and a piston coupled to the otherof said telescoped members and movably disposed in said internal borefor defining said fluid chamber.
 3. The well tool of claim 2 whereinsaid valve means include a valve seat defined in said passage means, avalve member movably disposed in said passage means and cooperativelyarranged for movement into and out of seating engagement with said valveseat, and actuating means operative upon relative movements between saidbody and said piston for moving said valve member into seatingengagement with said valve seat as said fluid chamber is expanded beyondsaid intermediate volume.
 4. The well tool of claim 2 wherein said valvemeans include a valve seat defined in said passage means, a valve membermovably disposed in said passage means and cooperatively arranged formovement into and out of seating engagement with said valve seat, andactuating means including first means normally biasing said valve membertoward seating engagement with said valve seat, an actuating memberoperatively arranged on said piston for retaining said valve member outof seating engagement with said valve seat until said body and pistonare relatively positioned where said fluid chamber is at its saidintermediate volume, and second means normally biasing said actuatingmember against said valve member until said body and piston arerelatively positioned where said fluid chamber has a volume equal to orgreater than said intermediate volume.
 5. The well tool of claim 1wherein said fluid-sampling means include sealing means cooperativelyarranged on said inner member and operatively associated with theinternal bore of said outer member for defining said fluid chamber. 6.The well tool of claim 5 wherein said valve means include a fluid sealcooperatively arranged on one of said telescoped members in said passagemeans and a sealing surface cooperatively arranged on the other of saidtelescoped members in said passage means and adapted for sealingengagement with said fluid seal to close said passage means uponmovement of said telescoped members for expanding said fluid chamberfrom said intermediate volume toward said increased volume.
 7. The welltool of Claim 1 wherein said means defining a fluid chamber include alongitudinal bore in said outer telescoped member, and a piston memberarranged on said inner telescoped member and disposed within saidlongitudinal bore for movement therein as said telescoped members aremoved between their said positions.
 8. The well tool of Claim 1 whereinsaid means defining a fluid chamber include a longitudinal bore in saidouter telescoped member having enlarged-diameter and reduced-diameterpOrtions, and a piston member arranged on said inner telescoped memberand disposed within said longitudinal bore for movement in said reducedbore portion upon movement of said telescoped members from their saidone position to their said other position and for movement from saidreduced bore portion into said enlarged bore portion upon movement ofsaid telescoped members from their said other position to an extendedposition.